fn main() {
    let a = 10;
    let b = a;
    let c = 15;
    // u32 占用4字节
    let sum = add(a, b);

    println!("{}", sum);

    // 事先不知道需要多少内存
    let msg = String::from("Hello");
    let msg2 = msg;
    println!("{}", msg2);
}

fn add(x: u32, y: u32) -> u32 {
    let res = x + y;
    res
}
